Heretofore, a dopant host method, a counter BN method, a thermal decomposition method, and the like have been known as methods for forming a p-type region on a silicon semiconductor substrate.
The dopant host method is a technique in which B2O3, which has volatilized from a B2O3-containing glass ceramic wafer (a dopant host) disposed so as to be in parallel with a semiconductor wafer such as a silicon wafer while maintaining a certain distance therefrom, is deposited on the semiconductor wafer, and a boron component is thermally diffused within a semiconductor substrate (see, for example, Patent Literature 1).
The counter BN method is a technique that has processes nearly identical to those of the dopant host method. The counter BN method is different from the dopant host method in that a boron nitride wafer that has been subjected to an activation treatment (a treatment to convert BN to B2O3) is used in place of the glass ceramic wafer.
The thermal decomposition method is a technique in which liquid BCl3, BBr3, or the like is evaporated by bubbling, deposited on a pre-heated semiconductor wafer, decomposed to give a B2O3-deposited coating, and then thermally diffused.
In the counter BN method, an activation treatment needs to be performed on a dopant host almost every time doping is carried out. In contrast, in the dopant host method, it is necessary to perform an activation treatment only once at the beginning, and subsequent activation treatments are almost unnecessary. Accordingly, use of the dopant host method allows the process cost of p-type region formation to be kept low. In the thermal decomposition method, gas is deposited on a semiconductor wafer, and it is therefore problematic in that, in the case where B2O3 is diffused in a large-diameter semiconductor wafer, a variation in the deposition amount is large. In contrast, the dopant host method is advantageous in that since a heat treatment is performed such that a glass-ceramic wafer having the same area as a semiconductor wafer is disposed so as to face the semiconductor wafer, a variation in boron component diffusion is suppressed.